Investigation of the photocatalytic activity of magnetically recoverable g-C3N4/CoFe2O4/Bi2MoO6 particles for purifying tetracycline antibiotics: synthesis, characterization, ecotoxicity analysis, and plant toxicity test.

To purify water polluted by tetracycline antibiotics, a new visible light-driven magnetically recoverable photocatalyst, g-C3N4/CoFe2O4/Bi2MoO6, was prepared in this study, and it effectively removed tetracycline antibiotics. Its rapid recycling was achieved by external magnets, which greatly increased material utilization. After four repeated uses, the degradation rate of tetracycline antibiotics by the g-C3N4/CoFe2O4/Bi2MoO6 composite photocatalyst remained at a high level, and the magnetic separation performance remained stable. Subsequently, it was further discovered that the degradation mechanism of this photocatalytic system was consistent with a double Z-type mechanism, which enabled two transport channels for photogenerated electrons, and was favorable for the separation of the photogenerated electron-hole pairs and prolonged the lifetime of the photogenerated carriers. The active substances playing an important role in the photocatalytic system were ˙O2- and h+. In addition, the possible intermediates in the photocatalytic process were detected by GC-MS analysis, and a degradation mechanism was proposed. The ecotoxicity of the degradation products and intermediates was evaluated using the Toxicity Estimation Software Tool (TEST), and the mung bean seed cultivation test was carried out to visually and efficiently illustrate that the g-C3N4/CoFe2O4/Bi2MoO6 photocatalyst can effectively degrade antibiotics, with low ecotoxicity of the degradation products. This provides a new idea for the removal of organic pollutants using light energy.

Simple Co-Precipitation of Iron Minerals for the Removal of Phenylarsonic Acid: Insights into the Adsorption Performance and Mechanism.

In this study, three kinds of iron minerals, ferrihydrite, hematite, and goethite, were prepared by a simple coprecipitation method for the adsorption and removal of phenylarsonic acid (PAA). The adsorption of PAA was explored, and the influences of ambient temperature, pH, and co-existing anions on adsorption were evaluated. The experimental results show that rapid adsorption of PAA occurs within 180 min in the presence of iron minerals, and the adsorption process conforms to a pseudo-second-order kinetic model. The isothermal adsorption of PAA by ferrihydrite, goethite, and hematite agrees with the Redlich-Peterson model. The maximum adsorption capacities of PAA are 63.44 mg/g, 19.03 mg/g, and 26.27 mg/g for ferrihydrite, goethite, and hematite, respectively. Environmental factor experiments illustrated that an alkaline environment will significantly inhibit the adsorption of PAA by iron minerals. CO32-, SiO32-, and PO43- in the environment will also significantly reduce the adsorption performance of the three iron minerals. The adsorption mechanism was analyzed by FTIR and XPS, which indicated that ligand exchange between the surface hydroxyl group and the arsine group leads to the formation of an Fe-O-As bond, and electrostatic attraction between the iron minerals and PAA played an important role in the adsorption.

Evaluation and Prediction on the Effect of Ionic Properties of Solvent Extraction Performance of Oily Sludge Using Machine Learning.

Oily sludge produced in the process of petroleum exploitation and utilization is a kind of hazardous waste that needs to be urgently dealt with in the petrochemical industry. The oil content of oily sludge is generally between 15-50% and has a great potential for oil resource utilization. However, its composition is complex, in which asphaltene is of high viscosity and difficult to separate. In this study, The oily sludge was extracted with toluene as solvent, supplemented by three kinds of ionic liquids (1-ethyl-3-methylimidazole tetrafluoroborate ([EMIM] [BF4]), 1-ethyl-3-methylimidazole trifluoro-acetate ([EMIM] [TA]), 1-ethyl-3-methylimidazole Dicyandiamide ([EMIM] [N(CN)2])) and three kinds of deep eutectic solutions (choline chloride/urea (ChCl/U), choline chloride / ethylene glycol (ChCl/EG), and choline chloride/malonic acid (ChCl/MA)). This experiment investigates the effect of physicochemical properties of the solvents on oil recovery and three machine learning methods (ridge regression, multilayer perceptron, and support vector regression) are used to predict the association between them. Depending on the linear correlation of variables, it is found that the conductivity of ionic liquid is the key characteristic affecting the extraction treatment in this system.

Properties of binary surfactant systems of nonionic surfactants C12E10, C12E23, and C12E42 with a cationic gemini surfactant in aqueous solutions.

Properties of binary surfactant systems of nonionic surfactants poly(ethylene oxide) (PEO) lauryl ethers (C(12)E(10), C(12)E(23), C(12)E(42)) with a cationic gemini surfactant, butanediyl-α,ω-bis(tetradecyldimethylammonium bromide) (14-4-14), have been investigated by Steady-state Fluorescence (FL), zeta potential, Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), Cryogenic Transmission Electron Microscopy (CryoTEM), and X-ray Diffraction (XRD). Through FL measurements, critical micelle concentration (CMC) of the three binary systems for different mixing mole fractions is determined and the values fall between those of pure constituent surfactants. Ideal CMC (CMC(ideal)), mole fraction in aggregates (X), interaction parameter (ß), activity coefficients (f(1) and f(2)), and excess free energy of mixing (ΔG(ex)) have been calculated. All these parameters indicate nonideal behavior and synergistic interactions between the constituent surfactants, which is explained in terms of electrostatic attraction between headgroups of constituent surfactants and reduction of electrostatic repulsion between headgroups of 14-4-14 due to the presence of nonionic surfactants. DLS, TEM and CryoTEM results show that nonionic surfactants facilitate the formation of larger aggregates. Micelles and vesicles in larger size compared with those of 14-4-14 coexist in the mixed solutions. Both surfactant composition and PEO chain length are found to play a strong effect on the properties of the binary systems.

Aggregation properties of a novel class of amphiphilic cationic polyelectrolytes containing gemini surfactant segments.

A novel class of amphiphilic cationic polyelectrolytes, poly(A-co-G)s, comprising of gemini type surfactant segment 1,3-bis(N,N-dimethyl-N-dodecylammonium)-2-propylacrylate dibromide (G) and acryloyloxyethyl trimethyl ammonium chloride (A), were synthesized. Their aggregation properties were investigated by employing fluorescence spectroscopy, dynamic light scattering, transmission electron microscopy, and ζ-potential measurements. For comparison, a series of polyelectrolytes containing a traditional single alkyl chain surfactant unit (acryloyloxyethyl-N,N-dimethyl-N-dodecylammonium bromide (D)), poly(A-co-D)s, were also synthesized and investigated. It was found that the critical aggregation concentration (cac) of poly(A-co-G)s is much lower than that of poly(A-co-D)s. The huge interpolymer aggregates (with a hydrodynamic radius of >450 nm) occur in poly(A-co-G)s aqueous solution, and the size of aggregates increases with the increase of the molar content of the gemini-type surfmer segment and the concentration of the copolymer. The size of aggregates in poly(A-co-D)s aqueous solution is much smaller than poly(A-co-G)s, which also increases with the increase of the molar content of the single alkyl chain surfmer segment and the concentration of the copolymer. The results of aggregation number and charge density of aggregate in poly(A-co-G)s and poly(A-co-D)s indicate that the copolymers have a strong tendency toward interpolymer aggregation and the aggregates in poly(A-co-G)s are much more compact than those of poly(A-co-D)s. These results are interpreted in terms of the synergistic effects of double hydrophobic chains on the gemini surfactant unit.

The dynamic behavior of phycobilisome movement during light state transitions in cyanobacterium Synechocystis PCC6803.

Light state transition is a physiological function of oxygenic organisms to balance the excitation of photosystem II (PSII) and photosystem I (PSI), hence a prerequisite of oxygen-evolving photosynthesis. For cyanobacteria, phycobilisome (PBS) movement during light state transition has long been expected, but never observed. Here the dynamic behavior of PBS movement during state transition in cyanobacterium Synechocystis PCC6803 is experimentally detected via time-dependent fluorescence fluctuation. Under continuous excitation of PBSs in the intact cells, time-dependent fluorescence fluctuations resemble "damped oscillation" mode, which indicates dynamic searching of a PBS in an "overcorrection" manner for the "balance" position where PSII and PSI are excited equally. Based on the parallel model, it is suggested that the "damped oscillation" fluorescence fluctuation is originated from a collective movement of all the PBSs to find the "balance" position. Based on the continuous fluorescence fluctuation during light state transition and also variety of solar spectra, it may be deduced that light state transition of oxygen-evolution organisms is a natural behavior that occurs daily rather than an artificial phenomenon at extreme light conditions in laboratory.

Molecular properties of R-phycocyanin subunits from Polysiphonia urceolata in potassium phosphate buffer.

The two subunits of R-phycocyanin from Polysiphonia urceolata were isolated and renatured. The renatured subunits were characterized by electrophoresis, molecular weights and spectra. The blue-shifted spectra, fluorescence recovery and restoring of the energy transfer suggested correct refolding of the subunits. The molecular properties of the subunits in potassium phosphate buffer (KPB) were investigated in detail. The total fluorescence yields (Q(T)) of the beta subunit declined while the energy transfer efficiency (E(T)) in the beta subunit was promoted with the increase of KPB concentration. On the other hand, both Q(T) and E(T) were enhanced with the increasing of the subunit concentrations. Based on the structural information, the fluorescence quenching in high concentrations of KPB was ascribed to less rigid chromophores caused by the weakening of the hydrogen-bond interaction network, while the enhancement of the fluorescence and E(T) was due to the aggregation of the subunits in the ionic solvent. Aggregation was confirmed by cysteine-assisted promotion of renaturation yield and stability, as well as equilibrium unfolding tests. Optimal conditions were proposed for the refolding/unfolding studies, under which the subunits were mainly monomeric. Compared to that in C-PC, the blue-shifted spectrum of PCB in R-PC is suggested to bring larger energy transfer efficiency, probably due to the necessity of the light harvesting for P. urceolata living in deep water.